1. Field of the Invention
The present invention relates to a polarizing plate including a polarizer for linearly polarizing incident light and emitting the linearly polarized light, a display having the polarizing plate, and an electronic apparatus having the display.
2. Description of the Related Art
In liquid crystal displays and organic electroluminescence (EL) displays, transmitted light is optically modulated according to a picture signal inputted, or pixels are put into self-luminescence at luminances according to a picture signal, to thereby obtain a gradation on a pixel basis. A layer by which the transmitted light or the luminance of luminescence is modulated on a pixel basis will hereinafter be referred to as “modulating functional layer.” In the liquid crystal displays, the liquid crystal layer corresponds to the modulating functional layer, and in the organic EL displays, the organic EL layer corresponds to the modulating functional layer.
The light emitted from the modulating functional layer to the display surface (front surface) side undergoes two-dimensional optical modulation such that the brightness differs on a pixel basis, and, therefore, the light thus emitted serves as image display light with which a desired image is displayed.
The liquid crystal layer is not a light valve which perfectly shields light by itself. Therefore, it is usually necessary to dispose a (linearly) polarizing plate on each side in the thickness direction of the liquid crystal layer, i.e., on each of the backlight side and the display surface side of the liquid crystal layer, thereby raising the contrast to a level fit for practical use.
On the other hand, the organic EL layer is not luminous when no voltage is impressed thereon. Therefore, the organic EL display is capable of perfect black display, so that it is high in contrast. In this case, accordingly, a polarizing plate is not provided on the display surface side for the purpose of shielding the luminescence at the time of black display.
However, particularly in the case of an organic EL display for outdoor use, a phenomenon is liable to occur in which the reflection of ambient light by the internal metal wirings causes a lowering in contrast. Since the light reflected by the internal metal members is independent on the screen display and is generated even at the time of black display, it causes a lowering in contrast. In order to prevent a lowering in contrast from occurring due to such internal reflection, some organic EL displays have, for example, a combination of a (circularly) polarizing plate and a λ/4 plate on the display surface side. When the (circularly) polarizing plate and the λ/4 plate are combined, it is possible to secure a 90° directional change of linearly polarized light between the incident ambient light and the reflected light (the light which might go out on the same side as the incidence side after being reflected internally), so that the actual outgoing of the reflected light can be obviated.
In either of the two kinds of displays, a polarizing plate having a linearly polarizing function is disposed on the display surface side.
Such a display or an electronic apparatus having such a display may sometimes be used by a user wearing a pair of polarizing sunglasses. The pair of polarizing sunglasses is used for the purpose of shielding the polarized light components often outputted upon reflection of the sunlight on a variety of substances, thereby protecting eyes from the strong stimuli of the polarized light components, for example. Therefore, a pair of polarizing sunglasses is a kind of polarizing plate which has a transmission axis in a certain direction and an absorption axis in a direction orthogonal to the transmission axis.
When a display is viewed by a person wearing a pair of polarizing sunglasses, the presence of the polarizing plate on the display surface side may greatly lower the visibility of the display screen, depending on the angle of viewing.
Particularly in the case of a liquid crystal display, the arrangement angle of the polarizing plate on the display surface side has an extremely intimate relation with the display performance (luminance, contrast, viewing angle, etc.). Specifically, when the absorption axis in the polarizing plate on the display surface side has a rotational error in relation to the absorption axis in the liquid crystal layer underneath or in other polarizing plate, the display performance itself is likely to be lowered. Accordingly, it is difficult to enhance the visibility of the screen as viewed through a pair of polarizing sunglasses, without influencing the display performance at all.
Meanwhile, the number of functions of mobile apparatuses having a display has been increasing more and more, and the mobile apparatuses which are not only used for simply displaying character data but also frequently used as video image reproduction apparatuses for displaying television broadcasts, movies, etc. have appeared.
In such a mobile apparatus, characters being displayed are easier to look at when the screen is vertically oriented (portrait position), but the screen is desirably put into a widescreen position (landscape position) at the time of reproducing a video image. Therefore, such a mobile apparatus may be used with the screen turned into the portrait position or the landscape position according to the user's choice. Not only mobile apparatuses but also other apparatuses, for example, on-vehicle apparatuses are designed to be capable of such a switching of the screen into the portrait position and the landscape.
Since these apparatuses are used outdoors or at the automotive driver seat, their display screens have to retain a certain level of visibility as viewed from an arbitrary angle by a user wearing a pair of polarizing sunglasses. Accordingly, there is a need for a polarizing plate which ensures that the visibility differs little with variation in the angle of viewing.
In view of this, there has been known a technology in which a linear retarder having a very great retardation is adhered to the outermost surface of a polarizing plate on the display surface side, at a predetermined angle relative to the polarizing plate in the range of 30° to 60° (refer to, for example, Japanese Patent Laid-open Nos. 2004-170875 (hereinafter referred to as Patent Documents 1) and Hei 06-258634 (hereinafter referred to as Patent Document 2)).